I think this is the worst and biggest manmade environment disaster in the world, this happened in 1986 April 26 in Chernobyl. This disaster is the result of flawed reactor design that was operates with inadequately trained personnel. Actually this explosion is a Nuclear reaction and the steam explosion and radiation released more than 400 times in Hiroshima bomb. In this accident 2 Chernobyl plant workers died on that night and further 28 people reported as died because of radiation poisoning. Currently a 30 kilometer zone remains unoccupied around the nuclear plant, Resettlement is ongoing. Still people are suffering these disaster side effects.